THERMALLY ANNEALED GAN NUCLEATION LAYERS AND THE DEVICE-QUALITY METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION GROWTH OF SI-DOPED GAN FILMS ON (00.1) SAPPHIRE

The effect of epitaxial growth temperature (985-1050-degrees-C) on the properties of Si-doped GaN layers on self-nucleated (00.1) sapphire h as been investigated. Several device-related properties monotonically improve with increasing growth temperature, including (a) carrier dens ity and (b) volume fraction of heteroepitaxial domains. However, a num ber of equally important device-related properties show a local maximu m and include (a) optical second-harmonic generation intensity, (b) st ructural coherence, and particularly (c) surface morphology. The antec edents of the first class lie in increases in surface and bulk diffusi on and reductions in film defect incorporation and stress at the GaN/G aN (nucleation layer)/alpha-Al2O3 heterointerface. The second class ar ises from the quite limited range over which the thermally annealed Ga N nucleation layer stimulates pseudo-two-dimensional growth of the GaN overlayer.